1. Field of the Invention
The present invention relates generally to a readable/recordable data storage medium, and relates, more specifically, to a data storage medium on which various types of multimedia data, including video data, still picture data, and audio data are recorded. The invention also relates to an apparatus and a method that records information on or reproducing recorded information from such a data storage medium.
2. Description of Related Art
In addition to being used to store computer data, read-only disc media such as DVD (Digital Versatile Disc)-ROM discs (hereinafter referred to as “DVD-ROM” discs) is exploited for recording movies and other video images, photographs and other still images, and audio data (collectively referred to below as “AV data”). Phase change type rewritable media such as DVD-RAM discs with a storage capacity of several gigabytes have also recently become practical and widely available.
With practical development of MPEG (Moving Picture Experts Group) and MPEG-2 as international coding standards for digital AV content, decoders and encoders, DVD-RAM applications are expected to quickly grow from a storage medium for computer data to a recording and playback medium for audio and video (AV) data. More specifically, DVD-RAM media is expected to replace a magnetic tape as the preferred medium for recording and playing AV data.
A problem is how to use such high capacity optical disc to record AV data so as to achieve new functionality and performance greatly surpassing that offered by conventional AV equipment.
One of the greatest benefits of the disc format is a significant improvement in random accessibility. While tape media can be randomly accessed, several minutes are typically required to rewind a video tape. This is many times slower than the comparable seek time (approximately several 10 ms) of optical disc media. For practical purposes, tape is therefore not considered a random access medium.
Random accessibility also enables distributed recording of AV data to an optical disc, something that is not possible with conventional magnetic tape media. FIG. 1 is a block diagram of DVD recording device (below referred to as a DVD recorder or drive). The drive has optical pickup 11 that reads data from DVD-RAM disc 10, error correcting code (ECC) processor 12, one track buffer 13, switch 14 that switches input/output to track buffer 13, encoder 15 and decoder 16.
As shown in FIG. 1, data is recorded on DVD-RAM disc 10 in each sector as the smallest recording unit. Each sector holds 2 KB. Groups of 16 sectors form one ECC block, the data unit to which ECC processor 12 applies error correction processing.
Track buffer 13 is used to record AV data at a variable bit rate in order to record AV data more efficiently to DVD-RAM disc 10. More specifically, while DVD-RAM disc 10 read/write rate Va is a fixed rate, the bit rate Vb of the AV data varies according to the complexity of the content (e.g., images if the content is video). Track buffer 13 is used to absorb such difference of bit rate. Track buffer 13 can also be effectively used to supply AV data continuously to decoder 16 when the AV data is recorded in dispersed locations on DVD-RAM disc 10. Track buffer 13 also enables the AV data sent to encoder 15 to be recorded on the DVD-RAM disc.
The Universal Disc Format (UDF) file system is used on DVD-RAM discs in order to use high capacity DVD-RAM discs more effectively and enable access by personal computers (PCs). The UDF file system is described in detail in the Universal Disc Format Standard.
A typical setup of conventional AV equipment is described next. FIG. 2 shows a relationship between conventional AV equipment, media, and formats. If the user wishes to view a video tape, for example, the user normally inserts a video tape to a VCR and watches it on a television. To listen to music, the user inserts a CD into a CD player or compact stereo system with a built-in CD player, and listens to the music through speakers or headphones. With conventional AV equipment there has thus been a one-to-one relationship between a particular format (video or audio) and the media used for that format. This means that the user must change the media and AV equipment according to the content to be seen or heard, and is somewhat inconvenient.
With recent advances in digital technologies DVD video discs are increasingly used to deliver prepackaged software and digital satellite broadcasting services. These developments have been made possible by the digital technology revolution and particularly by the widespread adoption of MPEG standards.
FIG. 3 shows the MPEG stream used for DVD video discs and digital broadcasting. The MPEG standard has a hierarchical structure as indicated in FIG. 3. What is important to note here is that the MPEG system layer stream used by the final application is different in packaged media such as DVD video disc and communications media such as digital satellite broadcasting. The MPEG system layer stream for packaged media is called the “MPEG program stream” and transmits data in units referred to as “packs.” Each pack corresponds to one sector, the recording unit of DVD video discs, for example. As noted above, each sector holds 2048 bytes. The MPEG system layer stream for broadcast media is called the “MPEG transport stream” and transmits data in TS packet units of 188 bytes each due to ATM considerations.
It has been widely expected that MPEG, a digital coding technology for audio-video data, would make it possible to freely handle AV data independently of the media, but small differences such as those noted above have meant that AV equipment and media compatible with both packaged media and communications media do not exist at present. DVD-RAM and other types of high capacity optical discs are expected to eliminate the inconveniences of conventional AV equipment.
The introduction of an optical disc medium, on which both the MPEG transport stream and MPEG program stream can be recorded, has been desired since the introduction of digital satellite broadcasting.
A DVD recorder enabling the user to freely display and present various formats and content types using a single AV device as shown in FIG. 4 without being concerned with the specific format is desired. This is described more specifically below with reference to FIG. 5 which shows an exemplary menu screen presented by a DVD recorder. This menu enables the user to seamlessly select a (1) movie delivered via digital satellite broadcast, or a (2) morning serial drama or (3) World Cup final delivered via conventional television antenna, or a (4) Beethoven piece dubbed from a CD without the user being aware of the recording media or format.
The biggest obstacle to achieving this type of DVD recorder, using optical disc media widely considered to be the next-generation AV recording medium is, how to uniformly manage AV data and AV streams of different formats. Special management techniques are not needed to only manage already existing formats. However, using a management technique that is compatible not only with the many formats already in use but can also handle new formats likely to be introduced in the future is essential to achieving the type of DVD recorder described above.
Differences in the user interface resulting from whether different AV streams can be uniformly handled or not could lead to inconveniences similar to those presented by the related art, that is, requiring the user to operate the equipment with an awareness of the specific content or format. A major problem, therefore, is how the receiver handles AV stream data digitized by the sender, such as in digital broadcasting. More particularly, in order for the various functions provided by new digital satellite broadcasting services to be usable after broadcast content is recorded, that is, in order to enable time shift recording, it is essential to record the broadcast stream as it was broadcast. The MPEG transport stream enables multiple video streams to be multiplexed to enable multiple views.
It is also desirable to be able to time-shift record new digital broadcasts anticipated in the future even if certain aspects of the service content are as yet undefined.
The “entry point” is one example of a feature enabling digitally recorded AV data to be accessed at random, the greatest feature of a disc medium. There is also a growing need for the user to be able to set entry points at desirable points in the content so that these entry points can be directly accessed to start playback therefrom. However, there are also entry points that are automatically recorded by the disc recorder. Confusion arises when the user-defined entry points and automatically recorded entry points are mixed, and there is therefore a need for a data structure enabling these different entry points to be separately identified.